Color television projector



Nov. 29, 1949 c.- c. LARSQN 9 2,439,299

COLOR TELEVISION PROJECTOR Filed April 15, 1946 INVENTOR CHRISTIAN C.LARSON ATTORNEY Patented Nov. 29, 1949 UNITED STATES PATENT OFFICE cowsELEV N RQJE Christian C. Larson, Fort Wayne, Ind., assignor, by mesneassignments, to Farnsworth Research Corporation, a corporation ofIndiana Application April 1o, 1946, Serial No. 662,378 5 Claims. (Cl.Nil-5.4)

This invention relates to television systems and particularly to anoptical device for use in producing a television image in color. A colortelevision system which is commonly u d employs a sin e c thode r y tubefo oducing in succession a plurality of partial images. Each partialimage represents one of a number of primary color components of thetelevision subject. Each of these partial images is reproduced in blackandwhite on the screen of the tube. A colored discor drum is rotatedbetween the fluorescent screen of the cathode ray tube and the observer,so that as each black and white representation of one of the primarycolor cornponents of the subject is reproduced on the screen, acorrespondingly colored filter element of the di or d m s' iiwss he ob re a d t e screen. The final result is a colored reproduc tion of thetelevision subject.

All of such systems require, in the first place, a movable color filterdevice either in the term of a disc, a drum or the like. The filterapparatus m be rotated o otherwise mo e in si nr tial synchronism withthe successive reproduc tions of the partial'television images. Suchappar n it u s to operaa a relati high Speed r th d ice m st c ps-S etIsle: tiv ly l r n mb r Pi @9 91" fi t e eme ts it order to produce thedesired effects.

Ordinarily, a television receiver is provided with a cathode ray tubewhich, when'directly viewed, will produce only a relatively small p c:ture. It is becoming ihcreasingly desirable to Pr ct i es rmnsuch tubsi's t a a m: tively a e ture ma b P duc d vi ing screen. One of themost satisfact y ,opt s em' f r e i a t evis on mol s er a c on of thehm dt ame aus t $9 2 as: tent heretofore in astronomical telescopes andthe like. A

In orderto use a r fle tion pe 9 antics} s st suh a at sed nth lscbmi ina television receiver for projecting c,o images upon a viewing screen,it nsuallyhas been necessary to sacrifice a substantial portion .oi' thei t in -prop r i o su h, o t m sts tem. For example, in one pr osed ns'eof a Schmidt Optical system a c. 9 te r s oc P ajection receiver, acolor filter drum having e. great many color filters is rotated in closepros imity to the fluorescent screen of the cathode ray tube. Inasmuchas this screen must also face he spherical reflecting member of theoptical system, it has been .necessaryto thread the color fil r hro huitahlei ats-inilw salient reflector. Then when the desired color filteris passing before the screen of the cathode'ray tube, the proper 1ycolored light representing the'corre} spondin'gcolor component of thetelevision subject is projected onto the spherical reflector. In thatsection of the reflector through which the filter drum operates thedesired colored image is reflected back through other segments of thecolor drum. If the desired color is say red, the rays of light reflectedfrom the central portion of the reflector will impinge upon green and/or blue filter segments. The reflected red rays which impinge upon thesegreen and blue filter segments are absorbed to a great extent therebyand, therefore, do not materially impair the color relproduction.Alternatively, it has been proposed to mask these filter segments whchare not in use at any given instant so that the colored light raysreflected from the mirror will not impinge upon these segments. In anycase, a substantial portion of the spherical mirror is not used for theenlarged reproduction of the image. In other words, the otherwiseefficiently operating Schmidt optical system is not employed at maximumefiicie cy'.

It, therefore, is an object of this invention to provide an opticalsystem of the reflection type which will function at high efiiciency ina television projection system.

Another object of the invention is to provide optical apparatus for usein conjunction with a Schmidt optical system for projecting coloredtelevision images onto a viewing screen without materially reducing theefficiency of the Schmidt stem In accordance with this invention, thereis provided the usual concave reflecting mirror and preferably, inaddition, an aspherical correcting plate if the concave mirror isspherical as in the Schmidt camera. A number of cathode ray repro-ducing tubes are directed generally toward the central axis of thesystem at a point between the concave mirror and the focal surface areathereof. In addition, there are provided a number of plane reflectors,one for each tube, which are located relative to the concave mirror andto the respective tubes in such a manner that they will reproduce in thefocal surface area of the concalvemirror a plurality of virtual imagesexactly in register corresponding to each of the cathode ray tubescreens; In a color television system some or all of the images may beof different elementary colors.

For a better understanding of the invention, together with other andfurther objects thereof,

, 3 reference is made to the following description, taken in connectionwith the accompanying drawlugs, and its scope will be pointed out in thepended claims.

In the accompanying drawings:

Fig. 1 is a side elevational view showing diagrammatically one form ofapparatus embodying the invention; and

Fig. 2 is a sectional view taken on the line 2-2 of Fig. 1.

Having reference now to the drawings, there is shown a concave reflectorPref rably, as in the Schmidt camera, this reflector is spherical. Therealso is provided a light refractive device |2 such as a lens having aparticular configuration to correct for the spherical aberration of thereflector The corrector plate I 2 is located substantially coaxiallywith the spherical reflector and is spaced therefrom at such a distancethat it lies substantially in the same plane as the center of curvatureof the reflector. The spherical reflector has a predetermined focalsurface area which also has a spherical configuration and is representedby the broken line 53.

The optical system in accordance with this invention also is providedwith a pluralit of plane reflectors which, in the illustrativeembodiment, comprise three contiguous faces of a cubical member M. Theplane reflectors which are used comprise the faces 55, i6 and 5?. Allthree of these plane reflectors meet at a common point which is locatedon the central axis E8 of the projecting optical system. The planereflectors are located between the spherical reflector ii and its focalsurface area l3 and face 3'5..-

generally the concave reflecting surface of the spherical reflector.

The system also includes a plurality of cathode ray televisionreproducing tubes. In the case where three plane reflectors are used,there are employed three tubes l9, 2| and 22. The tube |9, for example,is arranged so that the fluorescent screen which is formed on the faceof the tube is directed toward the plane reflector E5. The tube I9 islocated at such an angle with respect to the plane reflector If) thatthe image of the fluorescent screen of the tube is reflected from theplane reflector l5 onto the spherical reflecting surface of thereflector H in such a manner that the light rays which impinge upon thereflector appear to originate at the focal surface area i3. In otherwords, the tube 59 and the plane reflector i5 are so located relative toone another and to the spherical reflector N that a virtual image of thefluorescent screen of the tube 59 is formed in the focal surface area Ina similar manner, the tubes 2i and are located respectively relative tothe plane reflectors i6 and H to effect reflected reproductions of theirfluorescent screens in the spherical reflector Ii. The tubes 25 and 22likewise are located so as to produce virtual images of their respectivescreens in the focal surface area [3.

Between the fluorescent screen of the tube i9 and the plane reflectorl5, there is mounted a color filter 23. Similarly placed color filters 2and 25 are provided in conjunction with the tubes 2| and 22respectively. Depending upon the particular mode of operation of such adevice, as will be explained in greater detail subsequently, the colorfilters 23, 24 and 25 each may be different from the others or each mayhave other forms to be described. In one form of the invention, thecolor filter 23 may be red, the filter 24 green, and the filter 25 blue,for example. In

7 conventional.

42 such a case the filters will be mounted in a sta-' tionary mamier infront of the associated tube SCIEGllS.

Inasmuch as there are provided a plurality of cathode ray tubes inaccordance with this invention, the fluorescent screens of these tubeseach may be formed by different phosphors so that the images reproducedon the screens may be in the desired elementary colors. In such a case,the color filters may be eliminated.

Referring now to a preferred mode of operation of the describedapparatus embodying the invention, assume that the color filters 23, 24and 25 are respectively red, green and blue. In such a case, the arestationary. The television communication system employed to operate thecathode ray tubes l9, 2| and 22 may be entirely Such a system operatesby transmitting in succession trains of video signals representingrespectively red, green and blue partial images of a subject. In such acase, the video signals representing the red partial image are impressedupon the tube I9. These signals produce on the screen of the tube l9, ablack and white representation of the red portion of the subject. Thelight emanating from the face of the tube passes through the red colorfilter 23 to produce a red colored partial image on the plane reflectorl5. By reason of the described relationship between the tube IS, theplane reflector I5 and the spherical reflector II, this red partialimage is projected by the optical system comprising the sphericalreflector H and the corrector plate l2 onto a viewing screen (notshown).

In like manner, the video signals representing the green portion of thesubject are impressed upon the cathode ray tube 2| which, in conjunctionwith its associated green filter 24, produces a green partial image onthe plane reflector l6.

Similarly, the video signals representing the blue portion of thesubject are impressed upon the tube 22 which in cooperation with itsassociated color filter 25 produces a blue partial image on the planereflector ll.

Inasmuch as the cathode ray tubes and the plane reflectors are locatedrelative to one another in the manner described to produce,respectively, virtual images of the fluorescent screens in the focalsurface area l3, all of the partial images will be reproduced on theviewing screen exactly in register.

In order to operate the tubes I9, 2| and 22 sequentially in the mannerdescribed, a switch which preferably should be electronic may be used totransfer the video signal circuit from one tube to another as thecorresponding color signals are received. Alternatively, three separatesignaling channels may be provided, one for each of the color componentsof the picture so that all of the video signals may be transmitted andreceived for each of the colors substantially simultaneously.

If the plane reflectors l5, l6 and H form three contiguous faces of acube as illustrated and described, the cathode ray tubes |9, 2| and 22will be arranged substantially as shown. In such a case, the image ofthe screen of the tube 9 which is reflected by the plane reflector l5will use less than the entire surface of the spherical reflectorSimilarly the tubes 2| and 22 each will not utilize the entire surfaceof the spherical reflector. However, other angular positions of theplane reflectors may be used as subsequently described, whereby greaterportions of the spherical reflector surface may be used by eachth tubeIt may be desiredto increasethe brilliancy of the reproduced picture. Inthis event, the received video signals 'may be applied simultaneously-toall of the tubes, This will necessitate the use of color filtersassociated with each of the tubes which will include all three colors.They will reguire rotation or other movementin the usual manner tocoincide with the image which is being reproduced by the tube. 1Synchronism between the moving color discs, drums or the like may beeffected-in the usual manner. Nevertheless, by means of the presentinvention the color filters may be located entirelyout of the path ofany reflected light rays.

It obviously is not necessary to employ plane reflectors which formthree faces of a cube. If such a structure is used, the planereflectors, of necessity, are mutually disposed at right angles. Otherangular relationships between the plane reflectors may be employedwithin the scope of this invention. For example, each of the reflectorsmay be placed more nearly in a plane perpendicular to the central axisIS. The cathode ray tubes associated with such reflectors will belocated closely to the spherical reflector H. In some cases, it may bedesirable to so position the plane reflectors that the cathode ray tubeswill be located behind the spherical reflector. In such a case, suitableapertures maybe provided in the spherical reflector to enable light tobe projected from the tube screen onto the associated plane reflector.In cases where the plane reflectors are set in planes more nearlyperpendicular to the central axis of the system, the light which isreflected therefrom will fall upon a greater surface area of thespherical reflector II. More efficient operation may be obtained in somecases by so locating the plane reflectors and their associated tubes.Substantially any desired location may be employed so long as therelationship between each of the plane reflectors and its associatedcathode ray tube is such that there is produced a virtual image of eachtube screen in the focal surface area I3.

Obviously, the apparatus embodying the present invention is not limitedto the use of three plane reflectors. Other numbers of plane reflectorseither greater or smaller may be used with equal facility in order toobtain special effects without departing from the spirit of theinvention.

While there has been described what, at present, is considered thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is aimed,therefore, in the appended claims to cover all such changes andmodifications as fall Within the true spirit and scope of the invention.

What is claimed is:

1. An image projecting device for a color television system comprising,a concave spherical reflector having a predetermined focal surface area,a plurality of plane reflectors angularly disposed relative to oneanother and facing said spherical reflector, a plurality of cathode raytelevision reproducing tubes having the fluorescent screens thereofdirected toward respective ones of said plane reflectors, said tubes andsaid plane reflectors being so located relative to one another and tosaid concave reflector as to produce virtual images of said fluorescentscreens substantially in re ister he focalsurface area of said concavereflector, and means for directins differentlycoloredlighti from each ofsaid plurality of tubeszonto its corresponding plane reflector.

2. An imageprojecting device for a color tele-i vision systemcomprising, a concave reflector having a predetermined focal surfacearea, an auxili-. ary reflecting device facing said. spherical re-yhector, said auxiliary reflecting device comprising apluralityofplane'reflectors, a pluralityof cathode ray television reproducingtubes having the fluorescent screens thereof directed toward re spectiveones of said plane reflectors, said tubes. and said plane reflectorsbeing so located relative to one another and to saidconcavezreflector asto. produce a plurality of virtual images of saidfluorescentscreens.substantially in register in the focal surface areaof said concave reflector, and means associated with each of three ofsaid tubes in conjunction with the corresponding plane reflector toproduce three partial images of said television subject in threedifferent colors.

3. An image projecting device for a color television system comprising,a concave spherical reflector having a predetermined focal surface area,a light refractive device facing said reflector for correcting thespherical aberration of said reflector, an auxiliary reflecting devicelocated between said spherical reflector and its focal surface area,said auxiliary reflecting device comprising a plurality of planereflectors symmetrically disposed around the central axis through saidspherical reflector and said refractive device, a plurality of cathoderay television reproducing tubes having the fluorescent screens thereofdirected toward respective ones of said plane reflectors, said tubes andsaid plane reflectors being so located relative to one another and tosaid spherical reflector to produce of plurality of partial virtualimages of a television subject in the focal surface area of saidspherical reflector, and colored light filters located between each ofsaid tubes and its corresponding plane reflector.

4. An image projecting device for a color television system comprising,a concave spherical reflector having a predetermined focal surface area,a lens facing said reflector and spaced therefrom for correcting thespherical aberration of said reflector, an auxiliary reflecting devicelocated between said spherical reflector and its focal surface area,said auxiliary reflecting device comprising three plane reflectorsangularly disposed relative to one another in a symmetrical manner aboutthe central axis through said spherical reflector and said lens, threecathode ray television reproducing tubes having the fluorescent screensthereof directed toward respective ones of said plane reflectors, saidtubes and. said plane reflectors being so located relative to oneanother and to said spherical reflector as to produce three respectivevirtual images of said flourescent screens in substantial register inthe focal surface area of said spherical reflector, and a differentlycolored light filter located between each of said tubes and itsassociated plane reflector.

5. An image projecting device for a color television system comprising,a concave spherical reflector having a predetermined focal surface area,a spherical aberration corrector plate facing said reflector and spacedtherefrom, an auxiliary reflecting device located between said sphericalreflector and its focal surface area, said auxiliary reflecting devicecomprising three plane reflectors mutually disposed at right angles, thecommon point of said three plane reflectors being located on the centralaxis through said spherical reflector and said corrector plate and beingpointed toward said spherical reflector with the plane reflectorsdisposed symmetrically about said axis, three cathode ray televisionreproducing tubes having the fluorescent screens thereof directed towardrespective ones of said plane reflectors, said tubes and said auxiliaryplane reflectors being located suitably relative to one another and tosaid spherical reflector to produce registering virtual images of saidfluorescent screens in the focal surface area of said sphericalreflector, and :a diflerently colored light filter element locatedbetween each of said tubes and the corresponding plane reflector.

CHRISTIAN C. LARSON.

8 REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Australia June 1, 1939

